Different regions of fluctuation conductivity in unirradiated and alpha-irradiated Bi2Sr2CaCu2O8+delta and (Bi,Pb)(2)Sr2CaCu2O8+delta superconductors

Radiation damage in Bi-2212 and (Bi0.92Pb0.17)-2212 superconducting pellets due to irradiation by 40 MeV He++-beam has been studied, as these two comp ounds differ with respect to lattice strain in their Bi-O and (Bi,Pb)-O lay ers. These samples were prepared with excess oxygen that accounts for their lowered superconducting transition temperature, T-c, of 59.5 and 64.5 K, r espectively. Irradiation to 8.14x10(15) He++/cm(2) raised T-c by 4.5 and 5. 5 K, respectively, and also their normal state resistivities. Excess conduc tivity analysis for the unirradiated and irradiated samples showed (i) a tr ansition of the conductivity fluctuation from 2D (lambda = 1.0) to 3D (lamb da = 0.5) behaviour, on cooling across a temperature T-0, and (ii) also the signature (lambda = 3.0) of critical fluctuations in a network of supercon ducting microregions, for temperatures below T-cr, where T-cr is seen to be 5 to 10 K lower than T-0. The rise in T-c has been explained from irradiat ion-induced removal of oxygen taking the hole concentration towards the val ue for the peak in T-c. (C) 2000 Elsevier Science B.V. All rights reserved.